The goal of this project is to make possible a molecular approach to cancer prophylaxis and therapy for some types of viral neoplasia, especially human leukemia, cancer of the breast, and other human neoplasia in which retrovirus information may be detected. Major findings to date are: (1) adenosine (A), cytidine (C), and guanosine (G) tracts are present in all retrovirus RNAs examined; (2) uridine (U) tracts are absent in retrovirus RNA; (3) C and G tracts present in retrovirus RNA are transcribed into complementary deoxzyguanosine (dG) and deoxycytidine (dC) tracts, respectively, in cDNA transcripts of retrovirus RNA; (4) the 3'-terminal poly(A) sequences are not transcribed into poly (dT) sequences; (5) no sequences of like nucleotides of greater than or equal to 10 bases in length are present in the DNA of nonmalignant human embryonic cells; (6) however, dCMP and dGMP tracts of greater than or equal to 5 bases in length are present in the DNA of spontaneously transformed and retrovirus infected human embryonic cells and in the DNA of retrovirus infected and transformed, as well as chemically transformed mammalian cells; (7) DNA from a variety of excised human tumors and from various human tumore cell cultures are to be examined for the presence or absence of tracts of dCMP and dGMP nucleotides.